Implement an influenza model #1249
Description
Motivation / Current Behaviour
We want to add support for multiple infectious diseases.
Enhancement description
Implement a model specifically for influenza infections.
Additional context
It could follow e.g. https://www.medrxiv.org/content/10.1101/2025.03.27.25324818v1
Checklist
- Attached labels, especially loc:: or model:: labels.
- Linked to project